1. Field of the Invention
The present invention relates to a light-quantity control apparatus, also called an aperture stop apparatus, which is used in optical apparatuses such as cameras and interchangeable lenses.
2. Description of the Related Art
Performance of such a light-quantity control apparatus (aperture stop apparatus) influences the quality of images captured by using optical apparatuses, and, particularly, the shape of an aperture (aperture shape) formed by aperture blades and through which light actually passes changes the shape of so-called blur and ghost. Specifically, an aperture shape close to a circular shape makes the shape of the blur and ghost circular, which provides natural images, but a rectangular or flat aperture shape significantly different from the circular aperture shape makes the shape of the blur and ghost rectangular or flat, which provides unnatural images. Such an aperture shape significantly different from the circular shape is likely to be formed when the aperture is formed by two aperture blades. Thus, Japanese Utility Model Laid-Open No. 02-048928 discloses an iris aperture stop apparatus that rotates a driving ring around an aperture to rotate multiple aperture blades and forms a polygonal aperture shape closer to a circular shape than to a rectangular shape. Moreover, Japanese Patent Laid-Open No. 2009-115831 discloses an aperture stop apparatus that forms a polygonal aperture shape closer to a circular shape than to a rectangular shape by a combination of paired linearly-slidable aperture blades and paired swingable (rotatable) aperture blades.